PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 535 



Diabase. "Greenstone." Iron Ore.] 



No. 764. DIABASE. 



See under No. 7U>. 



Ref. Annual Report, x, page 97. 



Meg. A medium-grained, dark, greenish-gray, diabase-like rock. 

 Mic. The section is essentially similar to that of No. 763 except for a coarser 

 grain and the fact that the hornblende fibres sometimes have a radial arrangement. 

 One section examined. 

 Age. Keewatin. u. s. G. 



No. 765. " GREENSTONE. " 



See under No. 760. Top of East Twin peak. 

 Ref. Annual Report, x, page 97. 



Meg. A compact, fine-grained, green rock. 



Mic. This section shows a fine-grained, confused aggregate in which green honi- 

 altered feldspar and quartz are the chief minerals. Magnetite, chlorite, 

 e, calcite and opaque gray material are also present. The original texture 

 of the rock has entirely disappeared. 



One section examined. 



Age. Keewatin. 



Remark. Nos. 761-765, except No. 762, which is a later dike diabase, are part 

 of the extensive " greenstone " terrane that forms the high range of hills south of 

 Ogishke Muncie lake. It is quite evident that Nos. 763 and 764 were originally 







diabase or closely related rocks. Nos. 761 and 765 are so highly altered that their 

 original nature is not certain, but from their general character, composition and 

 associations it seems quite probable that they also were originally diabases or 

 possibly basic tuffs. u. s. o. 



No. 766. IRON ORE. (Magnetic.) 



Prom a ferruginous belt in the slates on the portage from Fox lake to Ash lake, near the former lake; 

 S. W. M S. W. J4 sec. 25, T. 65-6 W* 

 Ref. Annual Report, x, page 98. 



Meg. A very fine-grained magnetic iron ore. 



Mic. The section shows a very fine-grained rock, consisting mainly of magnetite 

 with some quartz and a yellowish fibrous mineral which appears to be grunerite. 

 The section is crossed by a few minute veins which are composed of quartz or quartz 



* The locality references for the specimens collected on the trip from Ogishke Muncie lake south to lake Superior, at the 

 mouth of Poplar river (where there is now a postomce called Lutsen) specimens Nos. 786 to 796 are in some cases not as 

 accurate as could be desired, and when this is the case the locality is designated as " probably " or " perhaps," the latter word 

 being used when there is considerable uncertainty. When this trip was made by the senior author most all the townships had not 

 been subdivided, and it was thus impossible to locate oneself accurately. Since then these townships have been surveyed, and by 

 reference to the township plats it is possible to locate, with a fair degree of certainty, the points at which the different specimens 

 were collected. The location of these points has been made easier by the facts that, since the townships were surveyed, (1) The 

 junior author has been over the route from Ogishke Muncie lake to and beyond "the last lake in Frog Rock river" (Nos. 766 to 

 773), and (2) Dr. A. H. Elftman has kindly aided in this matter in that part of the route from Sawbill lake to the mouth of Poplar 

 river (Nos. 788 to 796). 



